Although hydraulic fracturing and horizontal drilling are now routinely used to dramatically improve the production of gas from source shale (i.e., unconventional shale gas) and to make shale gas production commercially profitable, there is a fundamental need for understanding the rock and fluid physics of source shale. A clear understanding of the formation and the fluid (including gas) inside the formation is required to evaluate the production potential of the shale. Among all the logging technologies available for source shale evaluation, Nuclear Magnetic Resonance (NMR) provides an accurate porosity estimation along with information related to the fluids and gases within the rock.
The physical properties of source shale that defines the NMR response are the pore size and pore wettability. Source shale contains inorganic matrix, organic kerogen, and different fluids inside the pores. There are multiple types of porosities with diverse sizes and wettabilities which can be partitioned into three groups based on their origin. Pores within the kerogen are in the size of nanometer to 100 nanometers and are hydrocarbon wet. The pores inside the inorganic matrix are approximately the size of the rock grains themselves and are in the range of sub-microns. These pores are largely water wet to fractionally (mixed) wet. The third type of porosity is that of the micro-fractures which are larger than microns in size and are normally water wet or fractionally water wet. It would be well received in the drilling industry if apparatus and method could be developed to understand the nature of the fluids and gases in the shale gas rock and relate it to the NMR data that can be obtained using downhole NMR instruments.